Space borne tropospheric nitrogen dioxide (NO₂) observations from 2005–2020 over the Yangtze River Delta (YRD), China: variabilities, implications, and drivers

Nitrogen dioxide (NO2) is mainly affected by local emission and meteorology rather than long-range transport. Accurate acknowledge of its long-term variabilities and drivers are significant for understanding the evolutions of economic and social development, anthropogenic emission, and the effectiveness of pollution control measures on regional scale. In this study, we quantity the long-term variabilities and the underlying drivers of NO2 from 2005 to 2020 over the Yangtze River Delta (YRD), one of the most densely populated and highly industrialized city clusters in China, using OMI space borne observations and the multiple linear regression (MLR) model. We have compared the space borne tropospheric results to the surface in-situ data, yielding correlation coefficients of 0.8 to 0.9 over all megacities within the YRD. As a result, the tropospheric NO2 column measurements can be used as representatives of near-surface conditions, and we thus only use ground-level meteorological data for MLR regression. The inter-annual variabilities of tropospheric NO2 vertical column densities (VCDs) from 2005 to 2020 over the YRD can be divided into two stages. The first stage was from 2005 to 2011, which showed overall increasing trends with a wide range of (1.91 ± 1.50) to (6.70 ± 0.10) × 1014 molecules/cm2·yr−1 (p < 0.01) over the YRD. The second stage was from 2011 to 2020, which showed over all decreasing trends of (−6.31 ± 0.71) to (−11.01 ± 0.90) × 1014 molecules/cm2·yr−1 (p < 0.01) over each of the megacities. The seasonal cycles of tropospheric NO2 VCDs over the YRD are mainly driven by meteorology (81.01 % – 83.91 %) except during winter when anthropogenic emission contributions are pronounced (16.09 % – 18.99 %). The inter annual variabilities of tropospheric NO2 VCDs are mainly driven by anthropogenic emission (69.18 % – 81.34 %) except for a few years such as 2018 which are partly attributed to meteorology anomalies (39.07 % – 91.51 %). The increasing trends in tropospheric NO2 VCDs from 2005 to 2011 over the YRD are mainly attributed to high energy consumption associated with rapid economic growth which cause significant increases in anthropogenic NO2 emissions. The decreasing trends in tropospheric NO2 VCDs from 2011 to 2020 over the YRD are mainly attributed to the stringent clean air measures which either adjust high energy industrial structure toward low energy industrial structure or directly reduce pollutant emissions from different industrial sectors.

Interannual Variability of BVOC Emissions in an Alpine City

Terpenoid emissions above urban areas are a complex mix of biogenic and anthropogenic emission sources. In line with previous studies we found that summertime terpenoid emissions in an alpine city were dominated by biogenic sources, but especially at lower temperatures the anthropogenic influences were non-negligible. Inter-seasonal emission measurements revealed consistency for monoterpenes and sesquiterpenes, but a large difference in isoprene between the summers 2015 and 2018. Standardized emission potentials for monoterpenes and sesquiterpenes were 0.12 nmol m-2 s-1 and 3.0·10-3 nmol m-2 s-1 in 2015 and 0.11 nmol m-2 s-1 and 3.4·10-3 nmol m-2 s-1 in 2018, respectively. Observed isoprene emissions were about four times higher in 2018 than in 2015. This factor decreased to 2.3 after standardizing isoprene emissions to 30 °C air temperature and photosynthetic active radiation (PAR) of 1000 μmol m-2 s-1. Based on emission model parameterizations, increased leaf temperatures can explained ~50 % of these differences, but standard emission potentials remained higher in 2018, when a heat wave persisted. Potential other reasons for the differences such as emission parameterization, footprint changes, water stress conditions and tree trimming are investigated.

Phytoremediation of chromium(VI) using Colocasia esculenta in laboratory scale constructed wetlands

The existing water is becoming polluted nowadays due to high anthropogenic emission of water. The phytoremediation technology is used to treat the contaminated soil and water which containing higher amount of pollutants. The water that contains heavy metals will cause water scarcity and affect on human health when human drink the water. In this study, Colocasia esculenta was chosen for the removal of Cr(VI) in water. The efficiency of C.esculenta in accumulates Cr(VI) in synthetic wastewater was evaluated. The effect of time and concentration of Cr(VI) were identified in this study. Cr(VI) concentration was determined using diphenylcarbazide method (DPC). Experiment were set up in Laboratory Scale Constructed Wetlands with varies the concentration of synthetic wastewater of 1, 2, 5, 10, 50, 500 and 1000 mg/L and was continued for 36 days. The result of removal percentage for the 1, 2, 5 and 10 mg/L reach 100% while for 50, 500 and 1000 mg/L only remove 99.99%, 94.79% and 55.84% respectively. Roots of C.esculenta are able to accumulate Cr(VI) in wastewater which with BCF value was 1.557 mg/L. The BCF value of roots were more than 1, represents the higher accumulation of metal in plant. Therefore, C.esculenta has potential to use in removing Cr(VI) in water.

Effects of urban functional fragmentation on nitrogen dioxide (NO2) variation with anthropogenic-emission restriction in China

Urban functional fragmentation plays an important role in assessing Nitrogen Dioxide (NO2) emissions and variations. While the mediated impact of anthropogenic-emission restriction has not been comprehensively discussed, the lockdown response to the novel coronavirus disease 2019 (COVID-19) provides an unprecedented opportunity to meet this goal. This study proposes a new idea to explore the effects of urban functional fragmentation on NO2 variation with anthropogenic-emission restriction in China. First, NO2 variations are quantified by an Autoregressive Integrated Moving Average with external variables-Dynamic Time Warping (SARIMAX-DTW)-based model. Then, urban functional fragmentation indices including industrial/public Edge Density (ED) and Landscape Shape Index (LSI), urban functional Aggregation Index (AI) and Number of Patches (NP) are developed. Finally, the mediated impacts of anthropogenic-emission restriction are assessed by evaluating the fragmentation-NO2 variation association before and during the lockdown during COVID-19. The findings reveal negative effects of industrial ED, public LSI, urban functional AI and NP and positive effects of public ED and industrial LSI on NO2 variation based on the restricted anthropogenic emissions. By comparing the association analysis before and during lockdown, the mediated impact of anthropogenic-emission restriction is revealed to partially increase the effect of industrial ED, industrial LSI, public LSI, urban functional AI and NP and decrease the effect of public ED on NO2 variation. This study provides scientific findings for redesigning the urban environment in related to the urban functional configuration to mitigating the air pollution, ultimately developing sustainable societies.